OStatus: save file records for enclosures

OStatus: save file records for enclosures
Also stripping id from foreign HTML messages (could interfere with UI) and disabled failing attachment popup for a.attachment links that don't have a proper id, so you can click through instead of getting an error.

Issues:
* any other links aren't marked and saved
* inconsistent behavior between local and remote attachments (local displays in lightbox, remote doesn't)
* if the enclosure'd object isn't referenced in the content, you won't be offered a link to it in our UI